power supply sequence circuit with general purpose power
TRANSCRIPT
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© 2017 ROHM Co., Ltd. No. 60AP001E Rev.001
2017.4
© 2019 ROHM Co., Ltd. No. 62AN008E Rev.001
AUGUST 2019
Application Note
Power Management / Power Supply IC
Power Supply Sequence Circuit with General
Purpose Power Supply IC
When supplying an LSI or electrical equipment such as an FPGA or DSP with multiple power supply systems, the order of turning
ON/OFF the power supplies may be specified. If this order is not followed, the equipment may not be turned ON normally or devices
may be damaged. The order of turning ON/OFF the multiple power supply systems is referred to as a power supply sequence. A
power supply sequence IC may be used as a dedicated device to control the power supply sequence. This application note proposes
a circuit that accomplishes the power supply sequence without using any dedicated power supply sequence IC, by using general
purpose power supply ICs that do not have the Power Good output or an output discharge function required for the sequence control.
Power supply sequence specification 1
In this example, we introduce the circuit design for the power
supply sequence of 3 systems.
The specifications of the input and output voltages are shown
below.
VIN: 5.0V
VOUT1: 1.2V
VOUT2: 3.3V
VOUT3: 1.5V
Figure 1-1 shows the power tree diagram. In this example, the
circuit is configured with 3 power supply ICs. The power supply
ICs are assumed to be switching regulators (DC/DC converters)
or linear regulators (LDO). As a function of the power supply IC,
an enable pin that can control the ON/OFF of the output is
required.
The power shall be turned ON in the order of VOUT1, 2, and 3,
and be turned OFF in the order of VOUT3, 2, and 1. Figure 1-2
shows the schematic diagram.
5V DCDC1
DCDC2
DCDC3
VOUT1
VOUT2
VOUT3
1.2V
3.3V
1.5V
Figure 1-1. Power tree
VOUT1: 1.2V
VOUT2: 3.3V
VOUT3: 1.5V
OU
TP
UT
VO
LT
AG
E
t
Figure 1-2. Schematic diagram of the power supply sequence
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© 2019 ROHM Co., Ltd. No. 62AN008E Rev.001
AUGUST 2019
Application Note Power Supply Sequence Circuit with General Purpose Power Supply IC
Control block diagram 1
Figure 1-3 shows the control block diagram. DCDC 1, DCDC 2,
and DCDC 3 are the power supply ICs of 3 systems. Each output
is controlled by the enable (EN) pin. Power Good 1 and 2 monitor
the output voltage of the DCDCs when the power is turned ON,
and output the “High” signal to the DCDC to be turned ON next
when the output voltage reaches the target voltage. Power Good
3 and 4 monitor the output voltage of the DCDCs when the
power is turned OFF, and output the “Low” signal to the DCDC
to be turned OFF next when the output voltage reaches the
target voltage. The Discharge blocks ensure the normal
operation of the power supply sequence by rapidly discharging
the electric charges stored in the output capacitor of the DCDCs
to decrease the voltage when the power is turned OFF. Note that,
in this block diagram, the logic is designed as Active High
between EN and VOUT of the DCDC blocks, between IN and
PGOOD of the Power Good blocks, and between IN and OUT of
the Discharge blocks. In addition, the PGOOD pin (output) of the
Power Good blocks and the OUT pin of the Discharge blocks are
of the open-collector or open-drain type.
PGOOD IN
VIN VOUT
EN
VOUT1
DCDC 1
Power Good 1
VIN VOUT
EN
VOUT2
DCDC 2
VIN VOUT
EN
VOUT3
DCDC 3
5.0V
Enable
D1
D2
D3
D4
D5
D6
RPULLUP
VIN
IN OUT
Discharge 1
PGOOD IN
Power Good 3
IN OUT
Discharge 2
PGOOD IN
Power Good 2
PGOOD IN
Power Good 4
IN OUT
Discharge 3
RPULLUP
RPULLUP
1.2V
3.3V
1.5V
RPULLDOWN
RPULLDOWN
0V
0V
0V
L L
L
L L
L L
L
L L
L
L
L L
L L
L L
L L
5.0V
Figure 1-3. Control block diagram
Let’s follow the sequence operation in order. For the initial values,
the Enable terminal is at the “Low” level and the outputs of the 3
DCDCs are zero. Figure 1-4 shows the operation in the first step
when the power is turned ON. First, the “High” voltage is applied
to the Enable terminal to turn ON the power supplies. The “High”
voltage is applied to the EN pin of DCDC 1 via diode D1 and
DCDC 1 is turned ON. When the output voltage of DCDC 1
increases from 0 V to 1.2 V, the output voltage of Power Good 1
switches from “Low” to “High”. Then, the voltage is applied to the
EN pin of DCDC 2 on the next stage. In addition, since the “High”
voltage is applied to the IN pins of Power Good 3 and Power
Good 4 via diodes D2 and D4, the PGOOD pins (output) are
maintained at high impedance.
PGOOD IN
VIN VOUT
EN
VOUT1
1.2V
DCDC 1
Power Good 1
VIN VOUT
EN
VOUT2
3.3V
DCDC 2
VIN VOUT
EN
VOUT3
1.5V
DCDC 3
5.0V
Enable
D1
D2
D3
D4
D5
D6
RPULLUP
VIN
IN OUT
Discharge 1
PGOOD IN
Power Good 3
IN OUT
Discharge 2
PGOOD IN
Power Good 2
PGOOD IN
Power Good 4
IN OUT
Discharge 3
RPULLUP
RPULLUP
L H L H
0V 1.2V
L H
0V
0V
5.0V
RPULLDOWN
RPULLDOWN
Figure 1-4. Operation when the power is turned ON: First step
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© 2019 ROHM Co., Ltd. No. 62AN008E Rev.001
AUGUST 2019
Application Note Power Supply Sequence Circuit with General Purpose Power Supply IC
Figure 1-5 shows the operation in the second step when the
power is turned ON. The “High” voltage is applied to the EN pin
of DCDC 2 and DCDC 2 is turned ON. When the output voltage
of DCDC 2 increases from 0 V to 3.3 V, the output voltage of
Power Good 2 switches from “Low” to “High”. Then, the voltage
is applied to the EN pin of DCDC 3 on the next stage.
PGOOD IN
VIN VOUT
EN
VOUT1
DCDC 1
Power Good 1
VIN VOUT
EN
VOUT2
DCDC 2
VIN VOUT
EN
VOUT3
DCDC 3
Enable
D1
D2
D3
D4
D5
D6
RPULLUP
VIN
IN OUT
Discharge 1
PGOOD IN
Power Good 3
IN OUT
Discharge 2
PGOOD IN
Power Good 2
PGOOD IN
Power Good 4
IN OUT
Discharge 3
RPULLUP
RPULLUP
L H
0V 3.3V
L H
1.2V
3.3V
1.5V
5.0V
5.0V
0V
1.2V
H
RPULLDOWN
RPULLDOWN
Figure 1-5. Operation when the power is turned ON: Second
step
Figure 1-6 shows the operation in the third step when the power
is turned ON. The “High” voltage is applied to the EN pin of
DCDC 3 and DCDC 3 is turned ON. The output voltage of DCDC
3 increases from 0 V to 1.5 V and all of the 3 power supply
systems are now operating.
PGOOD IN
VIN VOUT
EN
VOUT1
DCDC 1
Power Good 1
VIN VOUT
EN
VOUT2
DCDC 2
VIN VOUT
EN
VOUT3
DCDC 3
Enable
D1
D2
D3
D4
D5
D6
RPULLUP
VIN
IN OUT
Discharge 1
PGOOD IN
Power Good 3
IN OUT
Discharge 2
PGOOD IN
Power Good 2
PGOOD IN
Power Good 4
IN OUT
Discharge 3
RPULLUP
RPULLUP
L H
0V 1.5V
1.2V
3.3V
1.5V
5.0V
5.0V 1.2V
3.3V
H
RPULLDOWN
RPULLDOWN
Figure 1-6. Operation when the power is turned ON: Third step
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© 2019 ROHM Co., Ltd. No. 62AN008E Rev.001
AUGUST 2019
Application Note Power Supply Sequence Circuit with General Purpose Power Supply IC
Figure 1-7 shows the state of the main nodes when the power
supplies are operating.
PGOOD IN
VIN VOUT
EN
VOUT1
DCDC 1
Power Good 1
VIN VOUT
EN
VOUT2
DCDC 2
VIN VOUT
EN
VOUT3
DCDC 3
Enable
D1
D2
D3
D4
D5
D6
RPULLUP
VIN
IN OUT
Discharge 1
PGOOD IN
Power Good 3
IN OUT
Discharge 2
PGOOD IN
Power Good 2
PGOOD IN
Power Good 4
IN OUT
Discharge 3
RPULLUP
RPULLUP
1.2V
3.3V
1.5V
H H
H
H H
H H
H
H H
H
H
H H
H H
H H
H H
H
5.0V
1.2V
3.3V
1.5V
5.0V
RPULLDOWN
RPULLDOWN
Figure 1-7. State of main nodes when the power supplies are
operating
Next, we follow the sequence operation when the power is
turned OFF in order. Figure 1-8 shows the operation in the first
step when the power is turned OFF. First, the “Low” voltage is
applied to the Enable terminal to turn OFF the power supplies.
The “Low” voltage is applied to the EN pin of DCDC 3 via diode
D6 and DCDC 3 is turned OFF. At the same time, the “Low”
voltage is applied to the IN pin of Discharge 3 and the OUT pin
switches to low impedance. This causes a rapid transition of the
output voltage of DCDC 3 to 0 V. When the output voltage of
DCDC 3 decreases, the output voltage of Power Good 4
switches from “High” to “Low”. Then, the voltage is applied to the
EN pin of DCDC 2 and the IN pin of Discharge 2 on the previous
stage.
RPULLDOWN
PGOOD IN
VIN VOUT
EN
VOUT1
DCDC 1
Power Good 1
VIN VOUT
EN
VOUT2
DCDC 2
VIN VOUT
EN
VOUT3
DCDC 3
Enable
D1
D2
D3
D4
D5
D6
RPULLUP
VIN
IN OUT
Discharge 1
PGOOD IN
Power Good 3
IN OUT
Discharge 2
PGOOD IN
Power Good 2
PGOOD IN
Power Good 4
IN OUT
Discharge 3
RPULLUP
RPULLUP
1.5V 0V
H L
H L
H L
H L H L
H L H L
H L H L
H
1.2V
3.3V
1.5V
5.0V
5.0V 1.2V
3.3V
RPULLDOWN
Figure 1-8. Operation when the power is turned OFF: First step
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© 2019 ROHM Co., Ltd. No. 62AN008E Rev.001
AUGUST 2019
Application Note Power Supply Sequence Circuit with General Purpose Power Supply IC
Figure 1-9 shows the operation in the second step when the
power is turned OFF. The “Low” voltage is applied to the EN pin
of DCDC 2 and DCDC 2 is turned OFF. At the same time, the
“Low” voltage is applied to the IN pin of Discharge 2 and the OUT
pin switches to low impedance. This causes a rapid transition of
the output voltage of DCDC 2 to 0 V. When the output voltage of
DCDC 2 decreases, the output voltage of Power Good 3
switches from “High” to “Low”. Then, the voltage is applied to the
EN pin of DCDC 1 and the IN pin of Discharge 1 on the previous
stage.
RPULLDOWN
PGOOD IN
VIN VOUT
EN
VOUT1
DCDC 1
Power Good 1
VIN VOUT
EN
VOUT2
DCDC 2
VIN VOUT
EN
VOUT3
DCDC 3
Enable
D1
D2
D3
D4
D5
D6
RPULLUP
VIN
IN OUT
Discharge 1
PGOOD IN
Power Good 3
IN OUT
Discharge 2
PGOOD IN
Power Good 2
PGOOD IN
Power Good 4
IN OUT
Discharge 3
RPULLUP
RPULLUP
3.3V 0V
H L H L
H L
L
1.2V
3.3V
1.5V
5.0V
5.0V
0V
1.2V
L
RPULLDOWN
Figure 1-9. Operation when the power is turned OFF: Second
step
Figure 1-10 shows the operation in the third step when the power
is turned OFF. The “Low” voltage is applied to the EN pin of
DCDC 1 and DCDC 1 is turned OFF. At the same time, the “Low”
voltage is applied to the IN pin of Discharge 1 and the OUT pin
switches to low impedance. This causes a rapid transition of the
output voltage of DCDC 1 to 0 V. All of the 3 power supply
systems are now turned OFF.
PGOOD IN
VIN VOUT
EN
VOUT1
DCDC 1
Power Good 1
VIN VOUT
EN
VOUT2
DCDC 2
VIN VOUT
EN
VOUT3
DCDC 3
Enable
D1
D2
D3
D4
D5
D6
RPULLUP
VIN
IN OUT
Discharge 1
PGOOD IN
Power Good 3
IN OUT
Discharge 2
PGOOD IN
Power Good 2
PGOOD IN
Power Good 4
IN OUT
Discharge 3
RPULLUP
RPULLUP
1.2V 0V
H L
1.2V
3.3V
1.5V
5.0V
5.0V
0V
0V
L
RPULLDOWN
RPULLDOWN
Figure 1-10. Operation when the power supply is turned OFF:
Third step
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© 2019 ROHM Co., Ltd. No. 62AN008E Rev.001
AUGUST 2019
Application Note Power Supply Sequence Circuit with General Purpose Power Supply IC
VCC
PGOOD
IN
DLY
82
13k
GND OP.
VIN VOUT
GNDEN
VOUT1
1.2V
DCDC 1
IC1 BD4142HFV
VCC
PGOOD
IN
DLY
2.4k
10k
GND OP.
VIN VOUT
GNDEN
VOUT2
3.3V
DCDC 2
VIN VOUT
GNDEN
VOUT3
1.5V
DCDC 3
5.0V
47k
VPGOOD1 = VOUT1 × 90%
= 1.2×0.9
= 1.08V
47k
47k
47k
VCC
PGOOD
IN
DLY
GND OP.
VCC
PGOOD
IN
DLY
GND OP.100k
100k
Enable
10k 100
6 5 3
2
1 4
10k 47
6 5 3
2
1 4
10k 47
6 5 3
2
1 4
47k
47k
47k
47k
47k
47k Q1
EMX1
Q2
EMX1
Q3
EMX1
D1
D2
D3
D4
D5
D6
IC2 BD4142HFV
IC3 BD4142HFV
IC4 BD4142HFV
R1
R2
R3
R4 R5
R7
R8
R9
R10
R11
R12
R13 R14
R15
R16
R17
R18
R19
R20
R21
R22 R23
VPGOOD2 = VOUT2 × 90%
= 3.3×0.9
= 2.97V
RB510SM-30
RB510SM-30
RB510SM-30
RB510SM-30
RB510SM-30
RB510SM-30
VIN
15kR6
0.01μC1
0.01μC3
0.01μC5
0.01μC7
C2
C4
C6
C8
VPGOOD3 = 0.5V
VPGOOD4 = 0.5V
VIN
VIN
VIN
Figure 1-11. Example of a circuit that accomplishes the power supply sequence
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© 2019 ROHM Co., Ltd. No. 62AN008E Rev.001
AUGUST 2019
Application Note Power Supply Sequence Circuit with General Purpose Power Supply IC
Example of circuit 1
Figure 1-11 shows an example of a circuit that accomplishes the
power supply sequence. The DCDCs in the 3 systems are
assumed to be switching regulators (DC/DC converters) or linear
regulators (LDO). The DCDCs feature an enable (EN) pin that
can control the ON/OFF of the output.
The Power Good blocks use voltage detector IC BD4142HFV to
perform the Power Good function. Figure 1-12 features the main
part. This IC is equipped with a built-in hysteresis comparator
with the detection voltage of 0.5 V. The detection voltage can be
set using an external resistor. The detection voltage VPGOOD can
be calculated with Equation 1-1.
𝑉𝑃𝐺𝑂𝑂𝐷 =𝑅2 + 𝑅3
𝑅3× 0.5 [𝑉]
In the example shown in Figure 1-11, VOUT1 is 1.2 V and the
PGOOD of IC1 is set to output the flag when 90% of the output
voltage is reached. If the detection voltage is set to a higher
value such as 95%, the PGOOD output switches to “Low” when
the output voltage momentarily drops due to fluctuations in the
load, disadvantageously causing momentary interruptions to the
DCDCs in the subsequent stages. The detection voltage should
be determined after understanding the specifications of the
fluctuations in the load and the voltage drop. The detection
voltage at 90% is 1.2 V × 0.9 = 1.08 V. The resistor values can
be calculated from Equation 1 as follows.
𝑉𝑃𝐺𝑂𝑂𝐷 =(15 𝑘𝛺 + 82 𝛺) + 13 𝐾𝛺
13 𝑘𝛺× 0.5 V = 1.08 [𝑉]
Therefore, R2 is a series connection of 15kΩ and 82Ω and R3 is
13kΩ.
IN
+
4DELAY
0.5V
1
UVLO
3
5 2
R2
R3
VCCPGOOD
DLY GND
R1
Hysteresis: 10mV
0.01μFC1
C2
VCC
Power GoodVPGOOD
Figure 1-12. Power Good function configured with BD4142HFV
Since the tolerance is ±1.8% for the detection voltage of
BD4142HFV, the range of PGOOD is from 88.4% (= 90% ×
0.982) to 91.6% (= 90% × 1.018). In addition, since the
hysteresis is 10 mV, the detection release voltage is 88.2% (=
90% × (0.5 V - 10 mV)/0.5 V) and the range is from 86.6% (=
88.2% × 0.982) to 89.8% (= 88.2% × 1.018).
To delay the PGOOD flag, connect a capacitor to the DLY pin.
The delay time and the capacitance can be calculated with
Equation 1-2.
𝐶2 =𝑡𝐷𝐸𝐿𝐴𝑌
2 × 106 [𝐹]
On the other hand, the PGOOD IC2 and IC4 operate when the
power is turned OFF. The detection is released (the output of the
PGOOD switches from “High” → “Low”) when the output voltage
of the DCDCs decreases to approximately 0.5 V or lower.
The Discharge block is configured with transistors and resistors
as shown in Figure 1-13. The transistor in the first stage is a
simple inverter circuit, and the transistor in the second stage is
a switch of an open-collector. The resistance connected in series
to the collector is varied to adjust the fall time of the output
voltage.
10k 100
6 5 3
2
1 4
5V
47k
47k Q1
EMX1
R1
R2
R3 R4
IN
VIN VOUT
GNDEN
DCDC 1
Figure 1-13. Discharge circuit
The diodes at various locations are components for creating
logic operations. Since the “Low” voltage needs to be maintained
low, Schottky barrier diodes with low forward voltages are used.
(1-1)
(1-2)
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© 2019 ROHM Co., Ltd. No. 62AN008E Rev.001
AUGUST 2019
Application Note Power Supply Sequence Circuit with General Purpose Power Supply IC
Example of operation 1
Figure 1-14 shows an example of the operation of the circuit in
Figure 1-11. The voltage from the main power supply (VIN 5.0 V)
is always applied. To turn ON the power, switch the Enable pin
from “Low” to “High”. Then, the output is turned ON in the order
of VOUT1, 2, and 3 according to the specification initially created.
Next, to turn OFF the power, switch the Enable pin from “High”
to “Low”. The output is turned OFF in the order of VOUT3, 2, and
1.
Figure 1-14. Operation waveforms of the power supply
sequence
In this way, the power supply sequence can be accomplished
without using any dedicated power supply sequence IC, by using
general purpose power supply ICs that do not have the Power
Good output or an output discharge function required for the
sequence control.
0
1
2
3
4
Vo
lta
ge
[V
]
Enable
0
1
2
3
4
5
6
0 5 10 15 20
Vo
lta
ge
[V
]
Time [ms]
VIN_5.0V
VOUT1_1.2V
VOUT2_3.3V
VOUT3_1.5V
VIN 5.0V
VOUT1 1.2V
VOUT2 3.3V
VOUT3 1.5V
9/16
© 2019 ROHM Co., Ltd. No. 62AN008E Rev.001
AUGUST 2019
Application Note Power Supply Sequence Circuit with General Purpose Power Supply IC
Power supply sequence specification 2
In this example, we introduce the circuit design for the power
supply sequence of 3 systems.
The specifications of the input and output voltages are shown
below.
VIN: 5.0V
VOUT1: 1.2V
VOUT2: 1.5V
VOUT3: 3.3V
Figure 2-1 shows the power supply tree diagram. In this example,
the circuit is configured with 3 power supply ICs. The power
supply ICs are assumed to be switching regulators (DC/DC
converters) or linear regulators (LDO). As a function of the power
supply IC, an enable pin that can control the ON/OFF of the
output is required.
The power shall be turned ON in the order of VOUT1, 2, and 3,
and be turned OFF in the order of VOUT1, 2, and 3 as well. Figure
2-2 shows the schematic diagram.
5V DCDC1
DCDC2
DCDC3
VOUT1
VOUT2
VOUT3
1.2V
1.5V
3.3V
Figure 2-1. Power tree
VOUT1: 1.2V
VOUT3: 3.3V
VOUT2: 1.5V
OU
TP
UT
VO
LT
AG
E
t
Figure 2-2. Schematic diagram of the power supply sequence
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© 2019 ROHM Co., Ltd. No. 62AN008E Rev.001
AUGUST 2019
Application Note Power Supply Sequence Circuit with General Purpose Power Supply IC
Control block diagram 2
Figure 2-3 shows the control block diagram. DCDC 1, DCDC 2,
and DCDC 3 are the power supply ICs of 3 systems. Each output
is controlled by the enable (EN) pin. Power Good 1 and 2 monitor
the output voltage of the DCDCs when the power is turned ON,
and output the “High” signal to the DCDC to be turned ON next
when the output voltage reaches the target voltage. In addition,
when turning the power OFF, the “LOW” signal is output to the
DCDC to be turned OFF next when the target dropped voltage
is reached. The Discharge blocks ensure the normal operation
of the power supply sequence by rapidly discharging the electric
charges stored in the output capacitor of the DCDCs to decrease
the voltage when the power is turned OFF. Note that, in this block
diagram, the logic is designed as Active High between EN and
VOUT of the DCDC blocks, between IN and PGOOD of the
Power Good blocks, and between IN and OUT of the Discharge
blocks. In addition, the PGOOD pin (output) of the Power Good
blocks and the OUT pin of the Discharge blocks are of the open-
collector or open-drain type.
PGOOD IN
VIN VOUT
EN
VOUT1
DCDC 1
Power Good 1
VIN VOUT
EN
VOUT2
DCDC 2
VIN VOUT
EN
VOUT3
DCDC 3
5.0V
Enable
RPULLUP
VIN
IN OUT
Discharge 1
IN OUT
Discharge 2
PGOOD IN
Power Good 2
IN OUT
Discharge 3
RPULLUP
RPULLUP
1.2V
1.5V
3.3V
L
5.0V 0V
0V
0V
L
L L
L L
L
L L
L L
L
L L
Figure 2-3. Control block diagram
Let’s follow the sequence operation in order. For the initial values,
the Enable terminal is at the “Low” level and the outputs of the 3
DCDCs are zero. Figure 2-4 shows the operation in the first step
when the power is turned ON. First, the “High” voltage is applied
to the Enable terminal to turn ON the power supplies. The “High”
voltage is applied to the EN pin of DCDC 1 and DCDC 1 is turned
ON. When the output voltage of DCDC 1 increases from 0 V to
1.2 V, the output voltage of Power Good 1 switches from “Low”
to “High”. Then, the voltage is applied to the EN pin of DCDC 2
on the next stage.
PGOOD IN
VIN VOUT
EN
VOUT1
DCDC 1
Power Good 1
VIN VOUT
EN
VOUT2
DCDC 2
VIN VOUT
EN
VOUT3
DCDC 3
5.0V
Enable
RPULLUP
VIN
IN OUT
Discharge 1
IN OUT
Discharge 2
PGOOD IN
Power Good 2
IN OUT
Discharge 3
RPULLUP
RPULLUP
1.2V
1.5V
3.3V
L H L H
5.0V 0V 1.2V
L H
0V
0V
Figure 2-4. Operation when the power is turned ON: First step
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© 2019 ROHM Co., Ltd. No. 62AN008E Rev.001
AUGUST 2019
Application Note Power Supply Sequence Circuit with General Purpose Power Supply IC
Figure 2-5 shows the operation in the second step when the
power is turned ON. The “High” voltage is applied to the EN pin
of DCDC 2 and DCDC 2 is turned ON. When the output voltage
of DCDC 2 increases from 0 V to 1.5 V, the output voltage of
Power Good 2 switches from “Low” to “High”. Then, the voltage
is applied to the EN pin of DCDC 3 on the next stage.
PGOOD IN
VIN VOUT
EN
VOUT1
DCDC 1
Power Good 1
VIN VOUT
EN
VOUT2
DCDC 2
VIN VOUT
EN
VOUT3
DCDC 3
5.0V
Enable
RPULLUP
VIN
IN OUT
Discharge 1
IN OUT
Discharge 2
PGOOD IN
Power Good 2
IN OUT
Discharge 3
RPULLUP
RPULLUP
1.2V
1.5V
3.3V
H
5.0V 1.2V
L H
0V 1.5V
0V
L H
Figure 2-5. Operation when the power is turned ON: Second
step
Figure 2-6 shows the operation in the third step when the power
is turned ON. The “High” voltage is applied to the EN pin of
DCDC 3 and DCDC 3 is turned ON. The output voltage of DCDC
3 increases from 0 V to 3.3 V and all of the 3 power supply
systems are now operating.
PGOOD IN
VIN VOUT
EN
VOUT1
DCDC 1
Power Good 1
VIN VOUT
EN
VOUT2
DCDC 2
VIN VOUT
EN
VOUT3
DCDC 3
5.0V
Enable
RPULLUP
VIN
IN OUT
Discharge 1
IN OUT
Discharge 2
PGOOD IN
Power Good 2
IN OUT
Discharge 3
RPULLUP
RPULLUP
1.2V
1.5V
3.3V
H
5.0V 1.2V
1.5V
0V 3.3V
L H
Figure 2-6. Operation when the power is turned ON: Third step
12/16
© 2019 ROHM Co., Ltd. No. 62AN008E Rev.001
AUGUST 2019
Application Note Power Supply Sequence Circuit with General Purpose Power Supply IC
Figure 2-7 shows the state of the main nodes when the power
supplies are operating.
PGOOD IN
VIN VOUT
EN
VOUT1
DCDC 1
Power Good 1
VIN VOUT
EN
VOUT2
DCDC 2
VIN VOUT
EN
VOUT3
DCDC 3
5.0V
Enable
RPULLUP
VIN
IN OUT
Discharge 1
IN OUT
Discharge 2
PGOOD IN
Power Good 2
IN OUT
Discharge 3
RPULLUP
RPULLUP
1.2V
1.5V
3.3V
H
5.0V 1.2V
1.5V
3.3V
H
H H
H H
H
H H
H H
H
H H
Figure 2-7. State of main nodes when the power supplies are
operating
Next, we follow the sequence operation when the power is
turned OFF in order. Figure 2-8 shows the operation in the first
step when the power is turned OFF. First, the “Low” voltage is
applied to the Enable terminal to turn OFF the power supplies.
The “Low” voltage is applied to the EN pin of DCDC 1 and DCDC
1 is turned OFF. At the same time, the “Low” voltage is applied
to the IN pin of Discharge 1 and the OUT pin switches to low
impedance. This causes a rapid transition of the output voltage
of DCDC 1 to 0 V. When the output voltage of DCDC 1
decreases, the output voltage of Power Good 1 switches from
“High” to “Low”. Then, the voltage is applied to the EN pin of
DCDC 2 and the IN pin of Discharge 2 on the next stage.
PGOOD IN
VIN VOUT
EN
VOUT1
DCDC 1
Power Good 1
VIN VOUT
EN
VOUT2
DCDC 2
VIN VOUT
EN
VOUT3
DCDC 3
5.0V
Enable
RPULLUP
VIN
IN OUT
Discharge 1
IN OUT
Discharge 2
PGOOD IN
Power Good 2
IN OUT
Discharge 3
RPULLUP
RPULLUP
1.2V
1.5V
3.3V
H L H L
5.0V 1.2V 0V
H L
1.5V
3.3V
Figure 2-8. Operation when the power is turned OFF: First step
13/16
© 2019 ROHM Co., Ltd. No. 62AN008E Rev.001
AUGUST 2019
Application Note Power Supply Sequence Circuit with General Purpose Power Supply IC
Figure 2-9 shows the operation in the second step when the
power is turned OFF. The “Low” voltage is applied to the EN pin
of DCDC 2 and DCDC 2 is turned OFF. At the same time, the
“Low” voltage is applied to the IN pin of Discharge 2 and the OUT
pin switches to low impedance. This causes a rapid transition of
the output voltage of DCDC 2 to 0 V. When the output voltage of
DCDC 2 decreases, the output voltage of Power Good 2
switches from “High” to “Low”. Then, the voltage is applied to the
EN pin of DCDC 3 and the IN pin of Discharge 3 on the next
stage.
PGOOD IN
VIN VOUT
EN
VOUT1
DCDC 1
Power Good 1
VIN VOUT
EN
VOUT2
DCDC 2
VIN VOUT
EN
VOUT3
DCDC 3
5.0V
Enable
RPULLUP
VIN
IN OUT
Discharge 1
IN OUT
Discharge 2
PGOOD IN
Power Good 2
IN OUT
Discharge 3
RPULLUP
RPULLUP
1.2V
1.5V
3.3V
L
5.0V 0V
H L
1.5V 0V
3.3V
H L
Figure 2-9. Operation when the power is turned OFF: Second
step
Figure 2-10 shows the operation in the third step when the power
is turned OFF. The “Low” voltage is applied to the EN pin of
DCDC 3 and DCDC 3 is turned OFF. At the same time, the “Low”
voltage is applied to the IN pin of Discharge 3 and the OUT pin
switches to low impedance. This causes a rapid transition of the
output voltage of DCDC 3 to 0 V. All of the 3 power supply
systems are now turned OFF.
PGOOD IN
VIN VOUT
EN
VOUT1
DCDC 1
Power Good 1
VIN VOUT
EN
VOUT2
DCDC 2
VIN VOUT
EN
VOUT3
DCDC 3
5.0V
Enable
RPULLUP
VIN
IN OUT
Discharge 1
IN OUT
Discharge 2
PGOOD IN
Power Good 2
IN OUT
Discharge 3
RPULLUP
RPULLUP
1.2V
1.5V
3.3V
L
5.0V 0V
0V
3.3V 0V
H L
Figure 2-10. Operation when the power is turned OFF: Third
step
14/16
© 2019 ROHM Co., Ltd. No. 62AN008E Rev.001
AUGUST 2019
Application Note Power Supply Sequence Circuit with General Purpose Power Supply IC
VCC
OUT-IN
7.5k
VEE
VIN VOUT
GNDEN
VOUT1
1.2V
DCDC 1
IC1
BA8391G
VIN VOUT
GNDEN
VOUT2
1.5V
DCDC 2
VIN VOUT
GNDEN
VOUT3
3.3V
DCDC 3
5.0V
VH = VOUT1 × 90% = 1.2×0.9 = 1.08V
VTH = 0.79V
VL = 0.5V
47k
91k
68k
Enable
10k 47
6 5 3
2
1 4
10k 47
6 5 3
2
1 4
10k 47
6 5 3
2
1 4
100k
100k
100k
100k
100k
100k Q1
EMX1
Q2
EMX1
Q3
EMX1
R1
R2
R3
R4 R5
R8
R10
R11
R12
R13 R14
R19
R20
R21
R22 R23
VIN
1μC1
+IN
1
2
34
547k
9.1k
R6
R7
R922k
VCC
OUT-IN
9.1k
VEE
VH = VOUT2 × 90% = 1.5×0.9 = 1.35V
VTH = 0.925V
VL = 0.5V
R171μC2
+IN
1
2
34
547k
11k
R15
R16
R1822k
IC2
BA8391G
Figure 2-11. Example of a circuit that accomplishes the power supply sequence
15/16
© 2019 ROHM Co., Ltd. No. 62AN008E Rev.001
AUGUST 2019
Application Note Power Supply Sequence Circuit with General Purpose Power Supply IC
Example of circuit 2
Figure 2-11 shows an example of a circuit that accomplishes the
power supply sequence. The DCDCs in the 3 systems are
assumed to be switching regulators (DC/DC converters) or linear
regulators (LDO). The DCDCs feature an enable (EN) pin that
can control the ON/OFF of the output.
The Power Good block is configured with a non-inverting
hysteresis comparator as shown in Figure 2-12, and the
comparator IC BA8391G is used for the device. A large
hysteresis voltage is provided between the detection voltage
when turning ON the power (VH) and the detection voltage when
turning OFF the power (VL). This enables a single device to
detect both voltages when turning the power ON and OFF to
output the control signals.
-IN 1
4
5
2
VCC
OUT
VEE
RPULLUP
1μFC1
VCC
PGOOD
3+IN
R1
R2
R3R4
VTH
VL, VH
BA8391G
Figure 2-12. Power Good function configured with a non-
inverting hysteresis comparator
First, we look at VH, the detection voltage when turning ON the
power. In the example shown in Figure 2-11, VOUT1 is 1.2 V and
the PGOOD IC1 is set to output the flag when 90% of the output
voltage is reached. The detection voltage VH is 1.2 V × 0.9 =
1.08 V. Next, VL, which is the detection voltage when turning
OFF the power, is set to 0.5 V. At this voltage, parasitic elements
generally will not be turned ON even if reverse voltage is applied
between the power supplies.
The threshold voltage of the comparator (VTH) is set to the
midpoint between VH and VL as shown in Figure 2-13. The value
can be calculated with Equation 2-1.
𝑉𝑇𝐻 =(𝑉𝐻 − 𝑉𝐿)
2+ 𝑉𝐿 [𝑉]
=(1.08 − 0.5)
2+ 0.5 = 0.79 𝑉
PG
OO
D
VL VTH VH
L
H
Figure 2-13. Hysteresis voltage
In the circuit diagram shown in Figure 2-12, VTH is expressed by
Equation 2-2. Converting this to the equation for R2 gives
Equation 2-3.
𝑉𝑇𝐻 =𝑅2
𝑅1 + 𝑅2× 𝑉𝐶𝐶 [𝑉]
𝑅2 =𝑅1 × 𝑉𝑇𝐻
𝑉𝐶𝐶 − 𝑉𝑇𝐻 [Ω]
When R1 is 47kΩ and VCC is 5 V, R2 is 8.8kΩ according to the
following equation. Select the nominal resistor value of 9.1kΩ
from the E24 series.
𝑅2 =47𝑘Ω × 0.79𝑉
5𝑉 − 0.79𝑉= 8.8𝑘Ω ≅ 9.1kΩ
To cancel the input bias current, select R3 so as to have the
same impedance as the inverting pin. The value is 7.6kΩ
according to Equation 2-4, so select the nominal resistor value
of 7.5kΩ from the E24 series.
𝑅3 =1
1𝑅1
+1
𝑅2
=1
147𝑘Ω
+1
9.1𝑘Ω
7.6𝑘Ω ≅ 7.5𝑘Ω
The general calculations for obtaining VH and VL of a non-
inverting hysteresis comparator are described by Equations 2-5
and 2-6. Converting these to the equations for R4 and RPULLUP
gives Equations 2-7 and 2-8.
𝑉𝐻 =(𝑅3 + 𝑅4) × 𝑅2
𝑅4 × (𝑅1 + 𝑅2)× 𝑉𝐶𝐶 [𝑉]
𝑉𝐿 =(𝑅3 + 𝑅4 + 𝑅𝑃𝑈𝐿𝐿𝑈𝑃) × 𝑉𝑇𝐻 − 𝑅3 × 𝑉𝐶𝐶
𝑅4 + 𝑅𝑃𝑈𝐿𝐿𝑈𝑃 [𝑉]
𝑅4 =𝑅2 × 𝑅3 × 𝑉𝐶𝐶
(𝑅1 + 𝑅2) × 𝑉𝐻 − 𝑅2 × 𝑉𝐶𝐶 [Ω]
(2-1)
(2-2)
(2-3)
(2-4)
(2-5)
(2-7)
(2-6)
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© 2019 ROHM Co., Ltd. No. 62AN008E Rev.001
AUGUST 2019
Application Note Power Supply Sequence Circuit with General Purpose Power Supply IC
𝑅𝑃𝑈𝐿𝐿𝑈𝑃 =𝑅3 × (𝑉𝑇𝐻 − 𝑉𝐶𝐶) + 𝑅4 × (𝑉𝑇𝐻 − 𝑉𝐿)
𝑉𝐿 − 𝑉𝑇𝐻 [𝑉]
Substitute the constants obtained above into Equations 2-7 and
2-8 to determine the remaining values.
𝑅4 =9.1𝑘Ω × 7.5𝑘Ω × 5𝑉
(47𝑘Ω + 9.1𝑘Ω) × 1.08𝑉 − 9.1𝑘Ω × 5𝑉
= 22.6𝑘Ω ≅ 22𝑘Ω
𝑅𝑃𝑈𝐿𝐿𝑈𝑃 =7.5𝑘Ω × (0.79𝑉 − 5𝑉) + 22𝑘Ω × (0.79𝑉 − 0.5𝑉)
0.5𝑉 − 0.79𝑉
= 86.9𝑘Ω ≅ 91kΩ
The Discharge block is configured with transistors and resistors
as shown in Figure 2-14. The transistor in the first stage is a
simple inverter circuit, and the transistor in the second stage is
a switch of an open-collector. The resistance connected in series
to the collector is varied to adjust the fall time of the output
voltage.
10k 47
6 5 3
2
1 4
5V
100k
100k Q1
EMX1
R1
R2
R3 R4
IN
VIN VOUT
GNDEN
DCDC 1
Figure 2-14. Discharge circuit
Example of operation 2
Figure 2-15 shows an example of the operation of the circuit in
Figure 2-11. The voltage from the main power supply (VIN 5.0 V)
is always applied. To turn ON the power, switch the Enable pin
from “Low” to “High”. Then, the output is turned ON in the order
of VOUT1, 2, and 3 according to the specification initially created.
Next, to turn OFF the power, switch the Enable pin from “High”
to “Low”. The output is turned OFF in the order of VOUT1, 2, and
3.
Figure 2-15. Operation waveforms of the power supply
sequence
In this way, the power supply sequence can be accomplished
without using any dedicated power supply sequence IC, by using
general purpose power supply ICs that do not have the Power
Good output or an output discharge function required for the
sequence control.
0
1
2
3
4
Vo
lta
ge
[V
]
Enable
0
1
2
3
4
5
6
0 5 10 15 20
Vo
lta
ge
[V
]
Time [ms]
VIN_5.0V
VOUT1_1.2V
VOUT2_1.5V
VOUT3_3.3V
(2-8)
(2-9)
(2-10)
VIN 5.0V
VOUT1 1.2V
VOUT2 1.5V
VOUT3 3.3V
6
Notice
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N o t e s
The information contained herein is subject to change without notice.
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Although ROHM is continuously working to improve product reliability and quality, semicon-ductors can break down and malfunction due to various factors.Therefore, in order to prevent personal injury or fire arising from failure, please take safety measures such as complying with the derating characteristics, implementing redundant and fire prevention designs, and utilizing backups and fail-safe procedures. ROHM shall have no responsibility for any damages arising out of the use of our Poducts beyond the rating specified by ROHM.
Examples of application circuits, circuit constants and any other information contained herein are provided only to illustrate the standard usage and operations of the Products. The peripheral conditions must be taken into account when designing circuits for mass production.
The technical information specified herein is intended only to show the typical functions of and examples of application circuits for the Products. ROHM does not grant you, explicitly or implicitly, any license to use or exercise intellectual property or other rights held by ROHM or any other parties. ROHM shall have no responsibility whatsoever for any dispute arising out of the use of such technical information.
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